1. Field of the Invention
The present invention relates to a printhead and printing apparatus. Particularly, the present invention relates to a printhead configured by integrating, on the same substrate, a plurality of printing elements and a driving circuit for driving them, and a printing apparatus using the printhead.
2. Description of the Related Art
An inkjet printing apparatus is configured to print information on a printing medium by discharging ink from a plurality of small nozzles of a printhead in accordance with a print signal. The inkjet printing apparatus is advantageous because it can perform non-contact printing on a printing medium such as paper, easily prints in color, and is quiet.
In the printhead of the inkjet printing apparatus, a printing element (heater) is arranged at a portion communicating with an orifice for discharging an ink droplet. A current is supplied to the printing element to generate heat and heat ink. The film boiling resulting from the heating of ink causes an ink droplet to be discharged for printing. To drive the printhead, it is a common practice to divide an array of orifices into groups each of a plurality of orifices, and time-divisionally drive printing elements for each of the different blocks. In the printhead, many orifices and printing elements (heaters) can be easily arranged at high density, allowing a high-resolution printed image to be obtained.
Recent printheads need to implement color printing, have a large printing width, and print quickly. To meet these requirements, it is becoming popular for a printing apparatus to be equipped with a plurality of printheads with each printhead having a plurality of element substrates. Information about ink discharge driving conditions is transmitted as serial data or parallel data from the printing apparatus main body to each printing element substrate.
In this arrangement, if the number of element substrates or printheads increases, the numbers of wiring lines, connectors, and transfer paths for the element substrates or printheads also increase. As a result, the element substrate dimensions increase, the production cost rises, and the electrical reliability drops. An increasing number of signals transferred to the printhead and a longer transfer path may generate a print signal transfer error. Especially if a transfer error occurs in an image data signal or heat enable signal, printing may not be performed at an intended position or a heat enable signal having a pulse width different from a desired one may be generated, degrading the quality of a printed image. To prevent an increase in the number of signal lines and a complicated connection, a technique of cascade-connecting n element substrates, wiring lines between them, and the like has been developed (see Japanese Patent Laid-Open No. 2002-67290).
In Japanese Patent Laid-Open No. 2002-67290, the element characteristic output terminal and temperature sensor output terminal of each element substrate are cascade-connected to the element characteristic input terminal and temperature sensor input terminal of an adjacent element substrate, respectively. This allows serially reading out information data from all element substrates via the same signal path, which have been conventionally read out from the respective element substrates via different signal paths. With a smaller number of signal lines, data of the element characteristic and temperature of the element substrate, and information of a signal transfer error can be transmitted to the printing apparatus main body.
Japanese Patent Laid-Open No. 10-324045 discloses an arrangement in which a transfer error is detected by comparing image data signals on the control unit side of a printing apparatus and the printhead side. In Japanese Patent Laid-Open No. 10-324045, print data transferred from a head driving circuit is transferred to a shift register in the control unit of the printing apparatus and that in the printhead. The comparator of the printing apparatus compares the print data transferred to these shift registers, determining whether a transfer error has occurred. The transfer error determination result is fed back to the printing apparatus main body.
As described above, when the printing apparatus adopts an arrangement using a plurality of printheads or a plurality of element substrates, an increasing number of signal lines may raise the cost, and a signal transfer error may occur due to a long transfer path. It is, therefore, required to perform appropriate printing control by feeding back information about ink discharge driving conditions in real time to the printing apparatus main body while suppressing an increase in the number of wiring lines of the printhead.
In the technique disclosed in Japanese Patent Laid-Open No. 2002-67290, the number of wiring lines is decreased by cascade-connecting element substrates. However, as the number of element substrates increases, the amount of serially readout information also increases because pieces of information are serially read out from all element substrates. A long time is taken to read out all pieces of information, greatly delaying the printing operation. Thus, even if a signal transfer error is detected, it is difficult to output the information in real time and perform appropriate control.
In the technique disclosed in Japanese Patent Laid-Open No. 10-324045, the signal transfer error of each element substrate or printhead can be detected. However, when the number of element substrates or printheads increases, the number of wiring lines and the circuit scale increase.